The prevalence of overweight and obesity is increasing globally, which is thought to account for a substantial number of chronic diseases and cancers. Surgical treatment of obesity has been shown to be effective in long- term weight control, provide additional benefits to people with obesity-related diseases, and reduce relative risk of death. However, it is not universally available to all classes of obese people. The proposed research will closely examine the costs and effectiveness of bariatric surgery. The ultimate goal is to examine the appropriateness of current NIH guidelines and to inform insurance companies, patients, providers, and the government of the most cost-effective surgical treatment of obesity. The Research Specific Aims are to (1) examine the association between obesity, obesity-related comorbidities, and mortality; (2) evaluate the safety and effectiveness of bariatric surgery; (3) investigate the costs attributable to obesity-related diseases; and (4) conduct cost-consequence analyses of bariatric surgery. The research methodology includes econometric modeling (Research Specific Aim 1 and 3), meta-analysis (Research Specific Aim 2), microsimulation (Research Specific Aim 3 and 4), and cost-effectiveness analysis (Research Specific Aim 4). In order to successfully complete the proposed research, this project will also provide the applicant with mentoring by three experts who, in conjunction with didactic training, will enable the applicant to grow into an effective and independent health services research investigator and health economist in obesity prevention and control. The mentoring team and the applicant have worked together and identified three Career Development Aims: (1) to become an independent and externally-funded researcher; (2) to obtain working knowledge of obesity epidemiology and gastroenterology; (3) to enhance the quality of research by obtaining training in the areas of public health and quantitative modeling. These aims will be achieved through a variety of training strategies, including regular one-on-one meetings with each of three mentors who are experts in the relevant domains, didactic coursework, high-quality online training modules, and attendance at scientific conferences and workshops. The proposed research will provide preliminary data and results for several R21 and an R01 or equivalent applications. These projects will expand to examine other interventions to control obesity, e.g., exercise, diet, medications, and surgery and will be compared within a metric of intensity; alternatively, these projects will examine the relationship between obesity and cancer and how interventions to control obesity can alter this relationship.